1. Field of Invention
The present invention relates to an electrooptic device and an electronic apparatus having many electrical elements formed on a substrate that supports an electrooptic material. The invention also relates to a method for making such an electrooptic device. Specifically, the invention relates to examining electrical characteristics of the electrical devices formed on the substrate.
2. Description of Related Art
In related art electrooptic devices, such as liquid crystal devices and organic electroluminescent devices, many switching elements are formed on a substrate supporting an electrooptic material.
An example of such an electrooptic device is an active matrix liquid crystal device employing thin film transistors, hereinafter xe2x80x9cTFTs,xe2x80x9d as the pixel switching elements. In making the device, as shown in FIG. 20, components of a plurality of TFT array substrates 10 are formed on a large substrate 10e, and the large substrate 10e is cut along cutting lines 10f so as to prepare individual TFT array substrates 10 used in liquid crystal devices.
The regions sandwiched by the cutting lines 10f are generally used in the related art as inspection regions 10g to inspect pixel-switching TFTs 30 formed in a matrix inside pixel regions 10a of the TFT array substrates 10 and to inspect driving-circuit TFTs (not shown) that constitute driving circuits 101 and 104, as shown in FIG. 21.
In other words, the pixel-switching TFT 30 is formed in each of the pixels arranged in a matrix on each TFT array substrate 10. When the TFT array substrate 10 is of an internal driving circuit type, the driving circuits 101 and 104 are constituted from TFTs (not shown). In the related art, the process for forming these TFTs is also used to form an inspection TFT 30gxe2x80x2 functioning as an inspection pattern, a first inspection pad 31gxe2x80x2 electrically connected with a drain region of the inspection TFT 30gxe2x80x2, a second inspection pad 32gxe2x80x2 electrically connected with a source region of the inspection TFT 30gxe2x80x2, and a third inspection pad 33gxe2x80x2 electrically connected with a gate electrode of the inspection TFT 30gxe2x80x2 within the inspection region 10g. These processes are performed onto the large substrate 10eshown in FIG. 20, and one inspection TFT 30gxe2x80x2 is formed in the inspection region 10g near one TFT array substrate 10 (one-to-one correspondence).
The electrical characteristics of the inspection TFTs 30gxe2x80x2 are examined by bringing inspection terminals into contact with the inspection pads 31gxe2x80x2, 32gxe2x80x2, and 33gxe2x80x2 while they are mounted on the large substrate 10e. If the electrical characteristics of the inspection TFT 30gxe2x80x2 are satisfactory, those of the pixel-switching TFTs 30 formed in the corresponding TFT array substrate 10 are assumed to be satisfactory, and the TFT array substrate 10 is assembled into a liquid crystal device. On the other hand, if the inspection TFT 30gxe2x80x2 is found to be defective, the pixel-switching TFTs 30 formed in the corresponding TFT array substrate 10 are assumed to be defective, and this TFT array substrate 10 is discarded. As a result, the yield can practically be increased. Moreover, the position in the large substrate 10e that is likely to suffer from defects can be detected, and the results can be easily reflected in the manufacturing process.
However, in the related art, the region where the inspection TFT 30gxe2x80x2 is formed is distant from the region where the pixel-switching TFTs 30 and driving-circuit TFTs are formed. This is because the inspection TFT 30gxe2x80x2 is formed outside the region of the TFT array substrate 10, although the inspection TFT 30gxe2x80x2 is formed near the region where the TFT array substrate 10 is formed in the large substrate 10e. 
Accordingly, when the TFTs are formed using the semiconductor process, the results at the inspection TFT 30gxe2x80x2 may not correspond with the quality of the pixel-switching TFTs 30 and the driving-circuit TFTs due to variation in the characteristics of the TFTs resulting from the position in the substrate. Moreover, the pattern density in the region where the pixel switching TFT 30g and the driving-circuit TFTs are formed is significantly different from the pattern density in the region where the inspection TFT 30gxe2x80x2 is formed. Thus, when the TFTs are made using the semiconductor process, for example, the influence of the pattern density on exposure is significantly different between the region where the pixel-switching TFTs 30 and the driving-circuit TFTs are formed and the region where the inspection TFT 30gxe2x80x2 is formed. Because of this, in some cases, the inspection results at the inspection TFT 30gxe2x80x2 do not reflect the quality of the pixel switching TFTs 30 and the driving-circuit TFTs.
To address or overcome these problems, the present invention provides an electrooptic device and an electronic apparatus, in which electrical characteristics of many thin-film switching elements formed on a substrate to support an electrooptic material can be reliably inspected. The invention also provides a method for making the electrooptic device.
To address or overcome the above-described problems, the present invention provides an electrooptic device including a substrate to support an electrooptic material and an electrical-element-forming region formed on the substrate and including many thin-film switching elements, in which an inspection pattern to examine characteristics of the thin-film switching elements and inspection pads electrically connected to the inspection pattern are formed inside the electrical-element-forming region.
Moreover, the preset invention also provides a method for making an electrooptic device including a substrate to support an electrooptic material and an electrical-element forming region formed on the substrate and including many thin-film switching elements. The method includes forming an inspection pattern to inspect the electrical characteristics of the thin-film switching elements inside the electrical-element forming region simultaneously with forming the thin-film switching elements inside the electrical-element-forming region of the substrate, and forming inspection pads electrically connected to the inspection pattern; examining the electrical characteristics of the inspection pattern by placing inspection terminals into contact with the inspection pads; and manufacturing the electrooptic device using the substrates that have been determined to have satisfactory quality as a result of inspection.
In this invention, the inspection pattern to examine the thin-film switching element formed inside the electrical-element-forming region is formed inside the electrical-element-forming region, so that the thin film switching element to be examined and the inspection pattern used in actual measuring are disposed nearby. Thus, when thin-film switching elements, such as TFTs, are formed in a substrate by a semiconductor process, the electric characteristics of the thin-film switching element to be examined accurately corresponds with the electrical characteristics of the inspection pattern used in actual measuring, even when the characteristics of the TFT vary depending on the positions in the substrate. Moreover, the conditions, such as pattern density, are the same between the region where the thin-film switching elements, i.e., the objects of the inspection, are formed and the region where the inspection pattern is formed. This is because the inspection pattern used in actual inspection is formed in the electrical-element-forming region. Thus, for example, the effect of exposure on the pattern density is the same between the region where the thin-film switching element to be examined are formed and the region where the inspection pattern is formed. Thus, the correspondence between the electrical characteristics of the thin-film switching elements to be examined and the electrical characteristics of the inspection pattern used in actual measuring is highly accurate. Accordingly the electrical characteristics of the thin film switching element formed in the substrate to support the electrooptical material can be accurately inspected.
In this invention, the electrical-element-forming region is, for example, a pixel region in which pixels having pixel electrodes to drive the electrooptic material and pixel-switching active elements formed as the thin-film switching elements to drive the pixel electrodes are arranged in a matrix. In such a case, the pixel region generally has an effective pixel region and a dummy pixel region arranged at the external periphery of the effective pixel region are formed in the pixel region, the effective pixel region including a plurality of effective pixels, arranged in a matrix to display images, the dummy pixel region including a plurality of dummy electrodes covered with a light-shielding member so as not to directly contribute to display of images. In the present invention, the inspection pattern and the inspection pads are preferably formed inside the dummy pixel region.
In other words, in the method for making the electrooptic device, when pixel region in which pixels having pixel electrodes to drive the electrooptic material and pixel-switching active elements formed as the thin-film switching elements to drive the pixel electrodes are arranged in a matrix is formed as the electrical-element-forming region, the inspection pattern and the inspection pads are preferably formed at the peripheral region inside the pixel region. In such a case, when the electrooptical device is assembled using the substrate, the center region of the pixel region is an effective pixel region in which effective pixels to display images are arranged in a matrix, and the peripheral region inside the pixel region is a dummy pixel region covered with a light-shielding member, the dummy pixel region including dummy pixels that do not directly contribute to the display of images.
According to this structure, the pixel-switching TFTs as the thin-film switching element to be inspected are near the inspection pattern used in actual measuring are disposed nearby and at a position having the same pattern density. Thus, the electrical characteristics of the pixel-switching TFTs to be inspected and the electrical characteristics of the inspection pattern used in actual measuring show high correspondence. Thus, the electrical characteristics of the pixel-switching TFTs formed in the pixel region of the substrate to support the electrooptic material can be accurately inspected. Moreover, because the inspection pattern and the inspection pads are disposed in the dummy pixel region in the pixel region, the number of the effective pixels to display images does not decrease.
In the present invention, a pixel-switching TFT, functioning as an active element for pixel switching, may be provided to each of the effective pixels and dummy pixels. The pixel-switching TFT may include a source region electrically connected to a data line, a drain region electrically connected to the pixel electrode, and a channel region opposing a gate electrode with an insulating film therebetween. Preferably, in such a case, the inspection pattern is formed in at least one of the plurality of dummy pixels, the inspection pattern including an inspection thin-film transistor having the same size and the same structure as the pixel-switching thin-film transistor. Preferably, in the dummy pixel region, a first inspection pixel in which the inspection thin-film transistor is formed is provided with a first inspection pad electrically connected to the drain region of the inspection thin-film transistor, a second inspection pixel adjacent to the first inspection pixel is provided with a second inspection pad electrically connected to the source region of the inspection thin-film transistor, and a third inspection pixel adjacent to the first inspection pixel is provided with a third inspection pad electrically connected to a gate electrode of the inspection thin-film transistor. With this structure, three inspection pads necessary to inspect the thin-film switching elements can have sufficiently large area.
In the present invention, the first inspection pad is preferably electrically connected, via a contact hole in an interlayer insulating film, to a drain electrode connected to the drain region of the inspection thin-film transistor. The second inspection pad is preferably electrically connected to an extended portion of the data line via a contact hole in the interlayer insulation film, the extended portion extending to the second inspection pixel. The third inspection pad is preferably electrically connected to an extended portion of the gate electrode via a contact hole in the interlayer insulation film, the extended portion extending to the third inspection pixel. With this structure, the step for making the pixel-switching TFTs in the pixel region can be used to form electrical connections between the inspection pads and the inspection TFTs.
In the present invention, when the TFT array substrate is of an internal-driving-circuit type, a pixel region in which pixels including pixel electrodes to drive the electrooptic material and pixel-switching thin-film transistors to drive the pixel electrodes are arranged in a matrix is formed in the substrate, and an electrical-element forming region is formed outside the pixel region, the electrical-element forming region including a driving circuit including many driving-circuit thin-film transistors as the thin-film switching elements to supply signals to the pixel switching thin-film transistors. When the driving circuit TFTs are examined for the TFT array substrate, the inspection pattern and the inspection pads are formed inside a driving-circuit forming region where the driving circuit is formed, and the inspection pattern is formed in a free region where no driving-circuit thin-film transistors are formed, the free region being inside the driving-circuit forming region. With this structure, the driving-circuit TFTs as the thin-film switching elements to be inspected and the inspection pattern used in actual measuring are disposed nearby and at a position having the same pattern density. Accordingly, the electrical characteristics of the driving-circuit TFTs to be inspected and the electrical characteristics of the inspection pattern used in actual measuring show high correspondence. Thus, the electrical characteristics of the driving-circuit TFTs formed in the driving-circuit region in the substrate for supporting the electrooptical material can be accurately determined. Moreover, since the inspection pattern is formed in the free region in the driving-circuit region, extension of the driving circuit is not necessary.
The inspection pattern used to examine the electrical characteristics of the driving-circuit TFTs preferably has the same structure and the same size as the driving-circuit TFTs.
In this invention, an example of the electrooptic material is liquid crystal held between the substrate and a counter substrate opposing the substrate with a predetermined gap therebetween.
The electrooptic devices of the present invention can used as display units of electronic apparatuses, such as mobile computers and cellular phones, for example.